Development of High-Hardness Wear-Resistant Crack-Resistant Surfacing Electrode for Cold Rolling Mill Repair

Overview of the Study

The paper by Li Wushen, Song Bingzhang, Feng Lingzhi, and Song Qingyi, published in China Mechanical Engineering in 1999 (Volume 10, Issue 11, pages 1305-1308), reports the development of a novel surfacing electrode designed specifically for the repair of 9Cr2Mo series cold rolling mill rolls. The work was supported by a Hebei Provincial Key Science and Technology Project and was conducted jointly by Tianjin University and Xingtai Special Rolling Mill. The core methodology employed a second-order rotational regression design (Box-Behnken type) to construct mathematical models correlating the deposited metal hardness and wear resistance with the composition of the electrode coating alloying agents. The resulting optimized electrode achieves a deposited metal hardness of HRC ≥ 60, exhibits excellent processability without preheating, and extends the service life of repaired rolls by 1 to 2 times compared to the original rolls.

Core Technical Methodology and Mathematical Modeling

The authors adopted a systematic approach rooted in experimental design methodology to optimize the electrode coating formulation. The second-order rotational regression design was selected because it efficiently captures both linear and quadratic effects of multiple alloying variables while maintaining experimental economy. The key response variables were the deposited metal hardness (measured in HRC) and the wear resistance of the surfacing layer, while the control factors were the types and proportions of alloying agents added to the electrode flux coating.

The mathematical model constructed from the regression analysis allowed the authors to identify the most influential alloying elements and their optimal weight percentages. By applying optimization techniques to the response surface model, the authors were able to predict the coating composition that would simultaneously maximize hardness and wear resistance while minimizing the risk of cracking in the deposited layer. This approach is particularly valuable because the development of surfacing electrodes traditionally relies on iterative trial-and-error, which is time-consuming and expensive.

Key Technical Parameters

The achievement of HRC ≥ 60 without preheating is particularly noteworthy from a metallurgical standpoint. High-carbon or high-alloy surfacing deposits are inherently susceptible to cracking due to the rapid cooling rates associated with arc surfacing, the high carbon and alloy content of the deposited metal, and the residual stresses developed during solidification. The electrode design must therefore balance the carbon and alloying element content to produce a hard, wear-resistant microstructure while managing the hydrogen content and residual stress levels to prevent cracking.

Metallurgical Considerations and Crack Prevention

The crack-free performance of the deposited layer without preheating is a critical engineering achievement. In high-hardness surfacing applications, the primary cracking mechanisms are solidification cracking (hot cracking) and hydrogen-induced delayed cracking (cold cracking). Solidification cracking is associated with the low melting point of eutectic phases at grain boundaries, while cold cracking is driven by the combination of high carbon equivalent, high residual stress, and diffusable hydrogen.

The electrode coating composition plays a decisive role in both mechanisms. The flux coating serves multiple functions: it stabilizes the arc, provides alloying elements to the deposited metal, controls the cooling rate, and desulfurizes and desiliconizes the weld pool. A properly designed coating can introduce elements such as manganese, silicon, and calcium that promote the formation of ductile inclusions and reduce the sulfur content, thereby inhibiting solidification cracking. Additionally, the coating can absorb hydrogen through reactions with elements like titanium or vanadium, reducing the diffusable hydrogen content and mitigating cold cracking risk.

From an engineering practice perspective, the elimination of the preheating requirement is a significant operational advantage. In rolling mill repair operations, downtime is extremely costly, and preheating large, massive rolls to elevated temperatures requires substantial energy input and extended preparation time. The ability to surfacing repair directly without preheating reduces repair cycle time and improves production efficiency.

Engineering Practice and Field Application

The field trial results demonstrate that the developed electrode effectively restores the wear resistance and spalling resistance of 9Cr2Mo cold rolling mill rolls. The 1 to 2 times life extension represents a substantial improvement in the cost-effectiveness of roll repair operations. In industrial rolling mill practice, roll surface degradation occurs through a combination of abrasive wear from the strip, adhesive wear from the rolling contact, and thermal fatigue cracking from the high-temperature rolling environment. The surfacing layer must therefore resist multiple wear mechanisms simultaneously.

The 9Cr2Mo steel is a martensitic hot-work steel with excellent hot hardness and thermal fatigue resistance. Its repair through surfacing requires the deposited metal to have a hardness and thermal stability comparable to the base material while maintaining sufficient toughness to resist spalling under the cyclic stresses of rolling. The developed electrode appears to meet these requirements, as evidenced by the improved spalling resistance reported in the field trials.

Reflections on Methodology

The use of mathematical modeling and optimization in electrode development represents a shift from empirical trial-and-error to a more systematic and predictive approach. This methodology reduces the number of experimental trials required, shortens the development cycle, and provides a deeper understanding of the structure-property relationships in the surfacing system. For engineers involved in welding consumable development, this approach offers a replicable framework that can be adapted to other surfacing applications requiring specific combinations of hardness, wear resistance, and processability.

The study also highlights the importance of considering the specific service environment of the repaired component. The 9Cr2Mo rolling mill application demands not only high hardness but also resistance to thermal cycling and mechanical spalling, which are distinct challenges from simple abrasive wear. A comprehensive understanding of the service conditions is essential for the rational selection of surfacing materials and processes.

Summary and Engineering Implications

This study demonstrates that a systematic approach combining experimental design, mathematical modeling, and optimization can successfully develop high-performance surfacing electrodes for demanding industrial applications. The achieved HRC ≥ 60 hardness without preheating, combined with crack-free deposition and 1 to 2 times service life extension, represents a meaningful engineering improvement for cold rolling mill roll repair. The methodology employed is broadly applicable to other surfacing consumable development challenges, and the results provide valuable reference data for engineers working on similar high-hardness, wear-resistant surfacing applications in heavy industry.